The present invention relates to vapor recovery canisters, and more particularly, to an improved vapor recovery canister for use in a fuel system.
Vapor recovery canisters serve to trap fuel vapor displaced during vehicle refueling operations as well as those created through a diurnal breathing loss (natural heating and cooling cycles). Specifically, vapor recovery canisters are in fluid communication with a fuel tank such that as pressure builds up in the tank caused by entering fuel or through a diurnal event, displaced fuel vapor disposed within the tank, will be treated prior to expulsion into the atmosphere. In this manner, the vapor recovery canister typically includes an adsorbent material, whereby the adsorbent material is operable to trap and store fuel vapor for future use. Once the adsorbent material has cleansed the air stream, and has sufficiently trapped the fuel vapor, the air stream may be released into the atmosphere.
After cleansing the air stream, the adsorbent material is loaded with fuel vapor which may be reused during the combustion process of a vehicle engine by purging the vapor recovery canister. In this regard, a conventional vapor recovery canister serves to cleanse a vapor laden air stream, thereby reducing fuel vapor emissions to the atmosphere. In addition, the vapor canister stores hydrocarbons from the captured fuel vapor for use in the combustion process of the engine, thereby improving the overall efficiency of the vehicle.
While adequately capturing fuel vapor from an air stream, a conventional vapor recovery canister suffers from the disadvantage of requiring a free flow into and out of the canister to ensure that the fuel tank can breathe freely during the purge cycle. In this regard, conventional vapor recovery canisters sacrifice a vacuum pressure, thereby reducing their efficiency. Therefore, a vapor canister that is exposed to a high vacuum during a purge cycle, thereby improving the working capacity of the canister, is desirable in the industry. Further, a vapor recovery canister which allows a fuel tank to maintain a predetermined pressure during a purging cycle, while concurrently providing an increased vacuum to the canister, is desirable in the industry.
Accordingly, the present invention provides a vapor recovery canister including an inlet port, an outlet port, and a first and second valve. The first and second valves are operable to restrict vapor flow into the canister, whereby the first valve is operable to selectively close the inlet port and the second valve is operable to selectively close the outlet port. In addition, one of the first or second valves includes at least one orifice formed therethrough for continuous fluid communication with an ambient air stream. In this manner, if either or both of the first and second valves are in a closed position, an air stream will be in fluid communication with an interior volume of the canister through interaction of the orifice, thereby causing the air stream to be in vacuum. By providing the canister with a continuous ambient air stream under high vacuum, the amount of hydrocarbons removed will increase. In this regard, the amount of hydrocarbons adsorbed during a load or purge cycle will increase, thereby reducing diurnal breathing emissions. In this regard, the introduction of high vacuum to the canister, when the first and second valves are in the closed position, increases the overall operation and efficiency of the canister.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.